tried 2 different loads with similar results. load 1 was a storebought 255 bbswc with 18gr./2400. load 2 was a 273 gr. ohaus swc sized to .454 with 18/2400. point of impact was a little different but group size was similar at 3.5 to 4 inches at 25 yds. this is comparable to 2 other 45 blackhawks from past years. my cylinder mouths measure .452 to .4525. bore size is . 4515 and area in front of forcing cone is .450. i've read the posts on borelapping over the last year but i haven't tried it. i understand about imbedding the grit in bullet surface and firing them at slow velocities. anyone have an idea about how many shots it may take to open up this constriction?